A variety of electrical connectors are designed for utilization with a flat flexible circuit which may be mounted directly on the connector or connected in circuit with terminal pins on the connector. Generally, a flat flexible circuit includes a flat flexible dielectric substrate having one or more holes therein for receiving one or more terminal pins. A ductile conductive film or other circuit trace system is deposited on the substrate in an area at least about the hole or holes. The terminal pins are inserted into the holes in the substrate to establish electrical and mechanical connections between the pins and the flat flexible circuit. Normally, each hole is smaller in diameter than a respective pin at the pin's widest portion. Alternatively, the pin may be punched through the flat flexible circuit to establish the electrical and mechanical connection therewith.
In order to assure good electrical and mechanical connections in these types of electronic devices or electrical connectors, solder or other adhesives often are used. For instance, in U.S. Pat. No. 4,970,624, dated Nov. 13, 1990 and assigned to the assignee of the present invention, uni-axial adhesive is deposited on the flexible circuit about the hole which is penetrated by the terminal pin. The adhesive includes a non-conductive base incorporating randomly spaced conductive particles. When the terminal pin is forced through the adhesive, a portion of the adhesive is carried with the terminal pin between the pin and the flat flexible circuit. The carried portion of the adhesive is compressed for establishing contact between the conductive particles and, thereby, conductivity between the terminal pin and the flat flexible circuit, leaving the adhesive other than that portion in a non-conductive state. Such adhesives often are called "Z-axis" adhesives. These adhesives were developed to replace soldering techniques which require specific temperature resistant components and substrates.
Conductive adhesives are used in other applications involving flat flexible circuits. For instance, in U.S. Pat. No. 5,456,616, dated Oct. 10, 1995 and assigned to the assignee of the present invention, the connector housing is fabricated of a die cast metallic material, such as of magnesium, aluminum or the like. The ductile film on the flat flexible circuit is fabricated of a different metallic material, such as copper or the like and, in fact, may be plated with still a different metallic material such as a tin/lead alloy. The conductive film on the flat flexible circuit acts as a ground plane against the rear face of the connector housing. The housing has a plurality of pins which project through holes in the flat flexible circuit. Using a "Z-axis" adhesive between the housing pins and the flat flexible circuit not only is expensive, as described above, but the conductive interface between the different metal components is limited to the areas of pressure. Consequently, the '616 patent teaches the use of an omni-directional conductive adhesive deposited on the conductive film over the areas of the holes therein, the conductive adhesive expanding the conductive interface between the metal housing and the metal ground plane defined by the conductive film.
Although such uses of conductive adhesives, whether the adhesives are Z-axis adhesives or omni-directional adhesives, serve their intended purposes in certain applications, they are relatively expensive both in the cost of the adhesives as well as their methods of use. In addition, the use of either type of conductive adhesive is costly in terms of secondary operations and costs associated with the metal particles, not to mention the problem of clogging adhesive dispensers by the metallic particles.
Because of the problems associated with the use of conductive adhesives, a unique system was devised as disclosed in U.S. Pat. No. 5,384,435, dated Jan. 24, 1995 and assigned to the assignee of the present invention. That patent solves the problems associated with conductive adhesives by eliminating the adhesive altogether and establishing an electrical connection directly between the terminal pin and the flat conductor on the flat flexible substrate. The electrical interface is established by controlling various parameters between the pin and the substrate. In the system disclosed in the '435 and '616 patents, the terminal pin is generally round in cross-section, and the round pin is inserted into a generally round hole in the flat flexible substrate. Although this system has proven quite effective in certain applications, there continues to be a need for further improvements in other applications, and the present invention is directed to that end.
In certain applications, for example, it has been found that a generally rectangular cross-sectional pin is preferred due to increased column strength or maintaining dimensions between adjacent pins. However, other applications are more suitable for generally round pins, and therefore there is a need to effect a reliable electrical connection in a given application for a pin with a variety of cross-sectional shapes. However, generally speaking, any pin shape can create problems by causing skiving of the coatings or platings along the length of the pin during insertion into a flexible circuit. That is, the controlled interference fit between the smaller hole in the flexible circuit and the larger pin can create skiving of the plating on either the pin or the circuit traces of the substrate during the insertion or assembly of the pin through the circuit. This skiving action can create conductive plating debris which can become loose and interfere with an electrical connection and is therefore highly undesirable in electronic devices. Furthermore, the skiving reduces the solderability of the pin coating which is also undesirable. The present invention is directed to solving the problems of skiving of the plating of the pin or the circuit substrate during assembly of the substrate.